The advancements in high performance of mobile communication devices such as mobile phones require acoustic wave devices, which are used as a filter, to reduce the size and height. Thus, the acoustic wave device may be formed as a wafer level package. A functional element that excites acoustic waves is sealed and protected in the acoustic wave device.
There is disclosed a technique that seals an IDT (Interdigital Transducer) with resin in Japanese Patent Application Publication No. 2008-135998 (Patent Document 1). There is disclosed a technique that seals the IDT with metal and resin in Japanese Patent Application Publication Nos. 2010-200198 and 2009-225118 (Patent Documents 2 and 3). There is disclosed a technique that seals the IDT with a cap wafer made of a piezoelectric substance, and provides a terminal piercing through the cap wafer in Japanese Patent Application Publication No. 2007-129704 (Patent Document 4). A boundary acoustic wave device is disclosed in Japanese Patent Application Publication No. 2007-28195 (Patent Document 5).
However, moisture resistance is not sufficient and heat release performance is low when the IDT is sealed with resin as disclosed in Patent Document 1. Low heat release performance causes low power durability. Resin is used in a part of a sealing portion in the technique disclosed in Patent Documents 2 and 3, and thus the moisture resistance and the heat release performance become low. The technique of Patent Document 4 needs a complicate fabrication process of the device including a process of providing a hole for extracting a terminal to a lid, and thus increases cost of the device. Only a terminal functions as a heat release path in the technique of Patent Document 5, and thus the heat release performance is not sufficient. The acoustic wave device may be embedded in a substrate. Heat of the acoustic wave device may be released by providing a via wiring for heat release to the substrate. However, a height of the terminal is different from that of a lid, and thus the process for providing the via wiring to the substrate becomes complicated and increases cost.